Several types of gas sensors, including electrochemical, surface acoustic wave (SAW), thermal conductivity and fiber optic sensors, are known in the art. As a class, fiber optic sensors have significant potential advantage over other sensing techniques. Their small size (3-1000 .mu.M) permits in-situ sensing; long-term stability can likely be achieved using silica or plastic fibers; remote sensing using a fiber optic network in which a fiber carries the signal to a central detector is possible; manufacturing and maintenance costs are low when standard optoelectronic components are utilized; the sensors, themselves, are non-electrical devices which may alleviate safety concerns; the sensors can be incorporated into a multi-site network; and the sensors are versatile, since the optical sensing method can use absorption (including reflectance and scattering), emission, or refractive index changes for detection; and it is possible in these optical methods to use different light frequencies.